This proposal aims to develop Luciferase-based imaging to enhance and extend studies of the interaction of CD8+ T cells with the liver, and in particular the intra-hepatic apoptosis of CD8+ T cells. These studies derive from a parent project, entitled "Peripheral T Cell Deletion in Liver" (5RO1-AI37554-09). To correctly interpret the mechanism of CD8+ T cell accumulation and apoptosis in the liver, it is essential to know where the T cells first encounter antigen. In Specific Aim 1, we will use a luciferase reporter that is linked to the IL-2 promoter, and thus expressed in activated T cells, to determine whether T cell activation is seen first in lymphoid tissue, or first in the liver. We will examine this using both an experimental model driven by exogenous peptide, and a model driven by an Adeno-Associated Virus Vector that is optimized to infect hepatocytes. The interaction of CD8+ T cells with the liver appears to involve direct recognition of antigen, and we hypothesize that aspects of this recognition involve Kupffer Cells. Therefore, in Specific Aim 2 we will use a transgenic Luciferase reporter for NF-kappaB to determine whether CD8+ T cells accumulating in liver cause Kupffer Cell activation. When activated CD8+ T cells are trapped in the liver at the end of an immune response, there is damage to hepatocytes, which we term "collateral damage" since it does not appear to involve direct CTL function against hepatocytes. Several lines of evidence suggest that Fas and FasL are involved in such damage, but it is not clear on which cells the FasL is expressed, nor whether the FasL expression is closely followed by hepatocyte death. Thus in Aim 3 we will use a transgenic Luciferase reporter driven by the FasL promoter to test when and in which cells F as L is expressed during collateral damage. The studies proposed are consistent with the exploratory/developmental nature of the R21mechanism, since we aim to use a newly-available imaging technology to study T cell accumulation, T cell activation, and the effect of T cells on the liver of mice. This method can be used to study individual experimental mice longitudinally, thus refining experimentation by reducing the total number of mice required to obtain data.